The objective of this research application is to explore the influence of viral exposure intensity during infancy on the development of asthma by age five years, and to identify critical time periods in infancy during which seasonal respiratory viral infection increases susceptibility to develop childhood asthma. Using the established research infrastructure of the Tennessee Medicaid claims data linked to birth certificates, we will determine the critical age periods associated with high risk of developing childhood asthma using a training dataset. The relationship of viral exposure intensity and infant age on development of childhood asthma will be examined in a separate test dataset. Furthermore, the potential interaction effects between infant viral exposure and maternal asthma (familial risk factor) and maternal smoking (environmental risk factor) will be examined. Restricted cubic splines will be applied to determine the smooth relationship between viral exposure age, intensity and the development of childhood asthma. The implications of this research relate to the potential for identifying critical time periods during which preventing infection could prevent or alter the phenotypic expression of asthma in predisposed hosts. [unreadable] [unreadable] [unreadable]